Methods and systems for translating virtual addresses in a virtual memory based system

ABSTRACT

An information handling system and method for translating virtual addresses to real addresses including a processor for processing data; memory devices for storing the data; a Page Walk Cache (PWC) for storing page directory entries; and a memory controller configured to control accesses to the memory devices. The processor in an embodiment is configured to send to the memory controller a page directory base and a plurality of memory offsets; and receive from the memory controller and store in the PWC at least one of the page directory entries. The memory controller is configured to: combine a first level page directory entry with a second level memory offset; read from memory a second page directory entry using the first level page directory entry and the second level memory offset; and send to the processor at least one of the page directory entries and a page table entry (PTE).

BACKGROUND

The disclosure herein relates generally to data processing, and moreparticularly, to methods, apparatus, and systems for optimizing addresstranslations in a computer system.

Among other tasks, memory management manages the data stored in acomputer including overseeing the retrieval and storage of data frommemory in a computer. Memory management is often a key factor in overallsystem performance for a computer. Computer systems often includephysical memory used to store applications and data. Modern computerstypically rely on a memory management technique known as virtual memorymanagement to increase performance and provide greater flexibility incomputers and the underlying architectural designs upon which they arepremised.

With a virtual memory system, the underlying hardware implementing thememory system of a computer is effectively hidden from the software ofthe computer. A relatively large virtual memory space is typically usedfor such a computer, with computer programs that execute on the computeraccessing the memory system using addresses pointing to locations in thevirtual memory space. The physical memory devices in the computer,however, are accessed via “real” addresses that map directly intospecific memory locations in the physical memory devices. Hardwareand/or software in the computer are provided to perform “addresstranslation” to map the virtual memory addresses of the of thevirtualized address space to real addresses in the physical memoryspace. As such, whenever a computer program on a computer attempts toaccess memory using a virtualized address, the computer translates thevirtualized address into a corresponding real address so that the accesscan be made to the appropriate location in the appropriate physicaldevice mapped to the virtualized address.

SUMMARY

The summary of the disclosure is given to aid understanding of acomputer system, computer architectural structure, processor, memorysystem, and method of translating virtual addresses in a computersystem, and not with an intent to limit the disclosure or the invention.The present disclosure is directed to a person of ordinary skill in theart. It should be understood that various aspects and features of thedisclosure may advantageously be used separately in some instances, orin combination with other aspects and features of the disclosure inother instances. Accordingly, variations and modifications may be madeto the computer system, the architectural structure, processor, andtheir method of operation to achieve different effects.

In one or more embodiments an information handling system is disclosed.The information system in an embodiment includes a processor forprocessing data; one or more memory devices having a plurality oflocations for storing the data, each location having a physical address;a Page Walk Cache (PWC) for storing a plurality of page directoryentries; and a memory controller, preferably local to the memorydevices, configured to control reading and writing accesses to thememory devices. The processor, in an aspect, in response to a request totranslate a first virtual address to a second address, is configured to:send from the processor to the memory controller a page directory baseand a plurality of memory offsets, wherein the plurality of memoryoffsets includes at least a first level memory offset and a second levelmemory offset; receive from the memory controller at least one of theplurality of page directory entries; and store in the PWC the at leastone of the plurality of page directory entries. The memory controller inan aspect is configured to: receive from the processor a page directorybase and a plurality of memory offsets; read from the one or more memorydevices a first level page directory entry using the page directory baseand the first level memory offset; combine the first level pagedirectory entry with the second level memory offset; read from the oneor more memory devices a second level page directory entry using thefirst level page directory entry and the second level memory offset; andsend to the processor at least one of the plurality of page directoryentries.

In one or more embodiments, in response to determining that all theplurality of memory offsets have been combined with the plurality ofpage directory entries, the memory controller is configured to send apage table entry (PTE) to the processor. The memory controller in anaspect is configured to send the first level page directory entry to theprocessor, and in a further aspect is configured to send the secondlevel page directory entry to the processor or both the first and secondlevel page directory entries. In an embodiment, the processor isconfigured to combine the page directory base and the first leveloffset, and to send the plurality of memory offsets together with thecombined page directory base and first level offset to the memorycontroller.

The memory controller in one or more embodiments is further configuredto fetch from the one or more memory devices a memory line containing anaddress of the first level page directory entry. In an aspect, thememory controller is further configured to extract from the memory linecontaining the address of the first level page directory entry, theaddress of the first level page directory entry. The system in an aspectis further configured to transmit the memory line containing the addressof the first level page directory entry from the memory controller tothe processor, and the processor is configured to extract from thememory line containing the address of the first level page directoryentry, the address of the first level page directory entry. Theprocessor according to an embodiment is further configured to store inthe PWC the first level page directory entry. The memory controller inone or more embodiments is further configured to fetch from the one ormore memory devices a memory line containing an address of the secondlevel page directory entry. The memory controller is further configuredaccording to an aspect to extract from the memory line containing theaddress of the second level page directory entry, the address of thesecond level page directory entry. The system is configured according toan embodiment to transmit the memory line containing the address of thesecond level page directory entry from the memory controller to theprocessor, and the processor is further configured to extract from thememory line containing the address of the second level page directoryentry, the address of the second level page directory entry. Theprocessor in an aspect is further configured to store in the PWC atleast one of the first level page directory entry, the second level pagedirectory entry, or both.

The memory controller, according to an embodiment, in response to thememory controller receiving the page directory base and the plurality ofmemory offsets, is configured to control all the memory readingoperations for the plurality of page directory entries stored in memoryand the system is configured so that all the memory reading operationsfor the plurality of page directory entries stored in memory originatein the memory controller. The system in one or more embodiments isconfigured so that all the plurality of memory offsets are transmittedtogether from the processor to the memory controller, and in an aspectthe memory controller is configured to combine the page directory baseand first level offset. The memory controller is configured in an aspectto transmit a page table entry (PTE) from the memory controller to theprocessor, wherein the PTE contains the translation of the first virtualaddress to the second address. The system is further configured in oneor more aspects to send a memory line from the memory controller to theprocessor that contains an address of a page table entry (PTE), and theprocessor is configured to extract from the memory line containing theaddress of the page table entry (PTE), the page table entry (PTE). Thememory controller is further configured in an embodiment to combine athird level offset with the second page directory entry and according toan aspect to read from memory a third level page directory entry usingthe third level offset and the second level page directory entry. Therequest to translate in one or more embodiments comprises a nestedtranslation having a guest virtual address and a host virtual address.

A computing system is also disclosed that includes a processor forhandling data; one or more memory devices having a plurality oflocations for storing the data, each location having a physical address;a Page Walk Cache (PWC) for storing a plurality of page directoryentries; and a memory controller configured to control reading andwriting accesses to the memory devices. In one or more embodiments thecomputing system also includes a computer-readable storage medium, andin an aspect a non-transitory computer-readable storage medium,comprising program instructions that when executed by the processor, inresponse to a request to translate a first virtual address to a secondaddress, cause the processor to send from the processor to the memorycontroller a page directory base and a plurality of memory offsets,wherein the plurality of memory offsets includes at least a first levelmemory offset and a second level memory offset; receive from the memorycontroller at least one of a plurality of page directory entries; andstore in the PWC the at least one of the plurality of page directoryentries. In an aspect the computing system also includes acomputer-readable storage medium, and in an embodiment non-transitorycomputer-readable storage medium, having program instructions that whenexecuted by the memory controller, in response to the request totranslate a first virtual address to a second address, cause the memorycontroller to receive from the processor a page directory base and aplurality of memory offsets; read from the memory devices a first levelpage directory entry using the page directory base and the first levelmemory offset; combine the first level page directory entry with thesecond level memory offset; and read from memory a second level pagedirectory entry using the first level page directory entry and thesecond level memory offset.

The computing system in an embodiment further has program instructionsthat when executed by the processor cause the processor to combine thepage directory base and the first level memory offset, and to send tothe memory controller the plurality of memory offsets together with thecombined page directory base and first level memory offset. The programinstructions in an aspect, when executed by the memory controller causesthe memory controller to fetch from the one or more memory devices amemory line containing an address of at least one of the first levelpage directory entry or the second level page directory entry (or both),wherein the memory line containing the address of at least one of thefirst level page directory entry or the second level page directoryentry (or both) is transmitted to the processor, and the processorfurther contains programming instructions that when executed by theprocessor causes the processor to extract from the memory line theaddress of at least one of the first level page directory entry or thesecond level page directory entry (or both) and to store in the PWC theaddress of the at least one of the first level page directory entry orthe second level page directory entry (or both).

A method of translating addresses by a system having a plurality of pagedirectory entries stored in memory is also disclosed. The method in anaspect includes in response to a request to translate a first virtualaddress to a second address, sending from a processor to a memorycontroller a page directory base and a plurality of memory offsets,wherein the plurality of memory offsets includes at least a first levelmemory offset and a second level memory offset; by the memorycontroller, reading from memory a first level page directory entry usingthe page directory base and the first level memory offset; combining thesecond level offset and the first level page directory entry by and inthe memory controller; by the memory controller, reading from memory asecond level page directory entry using the first level page directoryentry and the second level memory offset; sending at least one of thefirst level page directory entry or the second level page directoryentry to the processor; storing the at least one of the first level pagedirectory entry or the second level page directory entry in a Page WalkCache; and sending a page table entry (PTE) from the memory controllerto the processor. The method in an aspect is directed to a radix pagetranslation and the request to translate is directed to a radix pagetranslation where the plurality of page directory entries form part ofthe radix tree. The method in an aspect further includes combining inthe processor the first level memory offset with the page directorybase; and sending the remaining memory offsets together with thecombination of the page directory base and the first level memory offsetfrom the processor to the memory controller.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of exemplary embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects, features and embodiments of an information handlingsystem, a computer system, computer architectural structure, processor,memory system, and their method of operation will be better understoodwhen read in conjunction with the figures provided. Embodiments areprovided in the figures for the purpose of illustrating aspects,features, and/or various embodiments of the computer system, computerarchitectural structure, processors, and their method of operation, butthe claims should not be limited to the precise arrangement, structures,features, aspects, assemblies, systems, circuitry, embodiments, ordevices shown, and the arrangements, structures, subassemblies,features, aspects, methods, processes, circuitry, embodiments, anddevices shown may be used singularly or in combination with otherarrangements, structures, assemblies, subassemblies, systems, features,aspects, circuitry, embodiments, methods and devices.

FIG. 1 is a functional block diagram illustrating a computer system,according to embodiments of the present disclosure.

FIG. 2A depicts one example of a computing environment.

FIG. 2B depicts another example of a computing environment.

FIG. 3A depicts one example of a hierarchical translation mechanism.

FIG. 3B depicts one example of indexing of high-level translationtables.

FIG. 4 depicts another example of a hierarchical translation mechanism,according to embodiments of the present disclosure.

FIG. 5 illustrates a block diagram of a processor and memory controllerundergoing an embodiment of translating a virtual address.

FIG. 6 illustrates a block diagram of a processor and memory controllerundergoing another embodiment of translating a virtual address.

FIG. 7 illustrates a flowchart of an embodiment of a method oftranslating a virtual address to a physical address.

DETAILED DESCRIPTION

The following description is made for illustrating the generalprinciples of the invention and is not meant to limit the inventiveconcepts claimed herein. In the following detailed description, numerousdetails are set forth in order to provide an understanding ofinformation handling systems including computer systems, computerarchitectural structures, processors, memory systems, and their methodof operation, including methods of performing address translation,however, it will be understood by those skilled in the art thatdifferent and numerous embodiments of the information handling system,including computer systems, computer architectural structures,processors, memory systems, and their method of operation, includingmethods and structures for performing address translation, may bepracticed without those specific details, and the claims and disclosureshould not be limited to the embodiments, subassemblies, features,processes, methods, aspects, features or details specifically describedand shown herein. Further, particular features described herein can beused in combination with other described features in each of the variouspossible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc. It must also benoted that, as used in the specification and the appended claims, thesingular forms “a,” “an” and “the” include plural referents unlessotherwise specified, and that the terms “comprises” and/or “comprising,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

The following discussion omits or only briefly describes conventionalfeatures of information processing systems, including processors,microprocessor systems, memory systems, and their architectures, whichare apparent to those skilled in the art. It is assumed that thoseskilled in the art are familiar with the general architecture ofprocessors and memory systems and/or devices, and their operation. Itmay be noted that a numbered element is numbered according to the figurein which the element is introduced, and may be referred by that numberin succeeding figures.

In data and information handling systems there are numerous accesses todata stored in the various memory systems, including main memory.Accesses to memory in a virtualized memory system typically require anaddress translation from the virtual address (VA) to the real address(RA). Due to the frequency of memory access requests in a computer,address translation can have a significant impact on overall systemperformance. As such it is desirable to minimize the amount of time toprovide an address translation. This disclosure addresses this problemthrough systems and techniques to reduce the amount of time to provideaddress translation. In one or more embodiments a system and process forspeeding up Radix Page Translations (RPT) is disclosed, and inparticular RPT table walks by reducing the exchange of data between theprocessor (CPU) and memory, including the memory controller (MC), duringthe table walk translation process.

One feature of virtual addressing is that it not necessary for acomputer to include storage for the entire virtual memory space in thephysical memory devices in the computer's main memory. Instead, lowerlevels of storage, such as disk drives and other mass storage devicesmay be used as supplemental storage, with memory addresses grouped into“pages” that are swapped between the main memory and supplementalstorage as needed (“paging”). When the processing system uses paging,the low order bits of the virtual address are preserved and useddirectly as the low order bits of the actual physical address, while thehigh order bits may be treated as a key or index to one or more addresstranslation tables that correspond or map to physical addresses. Thememory referenced by such a range may be called a page. Page sizes mayrange in size, for example, from 4 Kilobytes to 16 Gigabytes.

Address translation in a virtual memory system typically incorporatesaccessing various address translation data structures. One suchstructure, referred to as a page table, includes multiple entries thatmap virtual addresses to real addresses on a page-by-page basis andincludes one or more page table entries (PTEs). Using virtualaddressing, processors can access memory using physical addresses thatare generated from translating virtual addresses (VA) to physical orreal addresses (RA).

The number of entries in a page table required to map all of the memoryaddress space in use by a computer can be significant, and requires theentries to be stored in Giga/Terabyte scale main memory (Random Accessmemory), rather than dedicated memory associated with the processor,which makes accessing such entries residing in main storage slow. Toaccelerate address translation, and reduce the latency with obtainingaddress translations, high speed memories associated with the processor,referred to as translation look-aside buffers (TLB), are typically usedto cache recently-used entries for quick access by the computer. A TLBis a data structure used to cache page table entries mapping virtualaddresses (VA) to physical addresses or real addresses (RA). With eachmemory access, the VA is presented to the TLB and if the TLB hits, i.e.,the VA of the memory access matches an entry in the TLB, the TLBprovides a real address (RA) to the processor. Finding a mapping ormatch in a given TLB provides a quick translation between a virtualaddress and a physical address.

Not finding a mapping or match for a virtual address in a given TLBindicates that the page table should be checked, and in one or moreembodiments that a table walk through multiple tables and levels willneed to be performed in order to translate the virtual address to a realaddress in physical memory. If the address misses in the TLB, in one ormore embodiments a translation process involving a more costly hardwarehandler or software handler is invoked to handle the translation, andload and insert the page table entry into the TLB so the address willhit in the TLB and the memory access can proceed. The TLB is usuallyassociated with and may be local to the processor (CPU).

There are several conventional approaches to translating virtualaddresses to real addresses in physical memory. Radix Page Translation(RPT) is a radix tree based approach for translating virtual addresses(VAs) to real addresses (RAs) in a virtual memory based system. The treestructured page tables (e.g., Radix address translation) approach uses atree structure in memory. The root of the tree is identified by aphysical address in memory, and bits from the virtual address are usedas an index at each level of the tree until a page table entry is found.While the final page table entry (PTE) found in the tree structure iscached in a TLB, the intermediate at each level typically are cached ina page walk cache (PWC). In a typical RPT translation it is necessary to“walk” through multiple levels of the radix tree in order to get thetranslated physical or real address (RA). In typical configurations thiswalking process is managed entirely by the processor (CPU) and can takea long time because of numerous exchanges between the processor (CPU)and the memory controller (MC).

Address translation typically occurs in a data or information handlingenvironment, and more specifically commonly in a processor based systemand/or a computerized environment. FIG. 1 is a functional block diagramillustrating a computer system 150 in which embodiments of thedisclosure may be practiced. The system 150 includes an example ofautomated computing machinery in the form of a computer 152.

The computer 152 may include at least one processor 156 or centralprocessing unit (“CPU”) as well as random access memory 168 (“RAM”),which is connected via a high speed memory bus 166 and bus adapter 158to the processor 156 and to other components of the computer 152.

Although the processor 156 is shown to be coupled to RAM 168 through thefront side bus 162, the bus adapter 158, and the high speed memory bus166, those of ordinary skill in the art will recognize that suchconfiguration is only an exemplary implementation and otherconfigurations of coupling the processor 156 to other components of thesystem 150 may be utilized. In some embodiments, the processor 156 maysupport direct peripheral connections, such as Peripheral ComponentInterconnect express (“PCIe”) connections and the like.

An operating system 154 may be stored in RAM 168 of the computer 152.Operating systems, useful in computers configured for operation of aprocessor, may include UNIX™, Linux™, Microsoft Windows™, AIX™, IBM'sz/OS™, and others known to those of ordinary skill in the art. Inaddition to the operating system 154 being located in RAM 168, othercomponents of such as data processing applications may be stored in theRAM 168. Furthermore, software and other components may be stored innon-volatile memory, such as on a disk drive 170.

The computer 152 may include a disk drive adapter 172 coupled through anexpansion bus 160 and bus adapter 158 to the processor 156 and othercomponents of the computer 152. The disk drive adapter 172 may connectnon-volatile data storage to the computer 152 in the form of the diskdrive 170. The disk drive adapter may include Integrated DriveElectronics (‘IDE’) adapters, Small Computer System Interface (‘SCSI’)adapters, and others known to those of ordinary skill in the art.Non-volatile computer memory may also be implemented as an optical diskdrive, electrically erasable programmable read-only memory (so-called‘EEPROM’ or ‘Flash’ memory), RAM drives, and others known to those ofordinary skill in the art.

The computer 152 may include one or more input/output (“I/O”) adapters178. I/O adapters 178 may implement user-oriented input/output through,for example, software drivers and computer hardware for controllingoutput to display devices, such as computer display screens, as well asuser input from user input devices 181, such as a keyboard and mouse.The computer 152 may include a video adapter 209, which is an example ofan I/O adapter specially designed for graphic output to a display device180, such as a display screen or computer monitor. Video adapter 209 isconnected to the processor 156 through the high speed video bus 164, busadapter 158, and the front side bus 162, which may also be a high speedbus. I/O adapters 178 may also include COMM and Drive adapters. I/Oadapters 178 may also be a PCI Express in which all I/Os are connected.

The computer 152 may include a communications adapter 167 for datacommunications with other computers 182 and for data communications witha data communications network 100. Such data communications may becarried out serially through RS-232 connections, through external busessuch as a Universal Serial Bus (“USB”), through data communicationsnetworks such as IP data communications networks, and in other waysknown to those of ordinary skill in the art. Communications adapter 167may implement the hardware level of data communications through whichone computer sends data communications to another computer, directly orthrough the data communications network 174. Examples of thecommunications adapter 167 may include modems for wired dial-upcommunications, Ethernet (IEEE 802.3) adapters for wired datacommunications, and 802.11 adapters for wireless data communications.

The arrangement of computers and other devices illustrated in FIG. 1 arefor explanation, not for limitation. Data processing systems usefulaccording to various embodiments of the present disclosure may includeadditional servers, routers, other devices, and peer-to-peerarchitectures. Networks in such data processing systems may support manydata communications protocols, including, for example, TCP (TransmissionControl Protocol), IP (Internet Protocol), HTTP (HyperText TransferProtocol), WAP (Wireless Access Protocol), HDTP (Handheld DeviceTransport Protocol), and others known to those of ordinary skill in theart. Various embodiments of the present disclosure may be implemented ona variety of hardware platforms, in addition to those illustrated inFIG. 1.

One example of a computing environment to incorporate and use one ormore aspects of the translation capability is described with referenceto FIG. 2A. In one example, a computing environment 100 includes aprocessor (central processing unit—CPU) 102 that includes at least onememory management unit (MMU)/translation lookaside buffer (TLB) portion104 and a cache 106. Processor 102 is communicatively coupled to amemory portion 108 having a cache 110, and to an input/output (I/O)portion 112. I/O portion 112 is communicatively coupled to external I/Odevices 114 that may include, for example, data input devices, sensorsand/or output devices, such as displays.

Memory management unit 104 is used in managing memory portion 108including facilitating access to the memory. To improve addresstranslation, the memory management unit in an embodiment utilizes atranslation lookaside buffer (TLB). The TLB is a cache of previouslytranslated addresses. Thus, when a request is received for a memoryaccess that includes an address to be translated, the TLB is checkedfirst. If the address and its translation are in the TLB, then notranslation is necessary. Otherwise, the received virtual address istranslated.

A further embodiment of a computing environment to incorporate and useone or more aspects of the present invention is depicted in FIG. 2B. Inthis example, a computing environment 150 includes a server 152 thatincludes, for instance, one or more virtual machines 154, one or morecentral processors (e.g., central processing units) 156, at least onehypervisor 158, and an input/output subsystem 160. The virtual machinesand hypervisor are included in memory 162.

In this embodiment, each virtual machine is capable of hosting a guestoperating system 168 and may be executing one or more applications 170.An operating system or application running in a virtual machine appearsto have access to a full complete system, but in reality, only a portionof it is available.

Central processors 156 (e.g., central processing units) are physicalprocessor resources that are assignable to a virtual machine. Forinstance, virtual machine 154 includes one or more logical processors,each of which represents all or a share of a physical processor 156 thatmay be dynamically allocated to the virtual machine. Central processor156, like CPU 102, includes at least one MMU/TLB portion and at leastone cache. Virtual machines 154 are managed by hypervisor 158, such asPowerVM, offered by International Business Machines Corporation, as anexample.

Input/output subsystem 160 directs the flow of information betweendevices and memory (also referred to herein as main memory or mainstorage). It is coupled to the server in that it can be part of theserver or separate therefrom. The I/O subsystem relieves the centralprocessors of the task of communicating directly with the I/O devicescoupled to the server and permits data processing to proceedconcurrently with I/O processing.

Address translation in a virtual memory system typically incorporatesaccessing various address data structures. One such structure, referredto as a page table, includes multiple entries that map virtual addressesto real addresses on a page by page basis. The format and informationincluded in the page table entry depends on the architecture of thesystem configuration and/or the specific type of translation. A pagetable entry located by traversing hierarchical page tables typicalincludes various information, including at least a portion of a realaddress used to access the physical memory.

The address received for translation may include virtual address bitsand one or more offsets, including a page offset. The virtual addressbits are transmitted to the TLB, which attempts to match the virtualaddress bits with a real page number stored in the TLB. If the TLB findsan entry containing a real page number matching the virtual addressbits, it provides a physical address. The physical address is used toaddress a page in the physical memory. The page bits or page offset isused to access an address relative to the beginning of the page.

In one embodiment, if a match is not found (TLB miss), the addresstranslation system fetches the physical address from the page table byperforming a page walk after a TLB miss. The virtual address resolutionsystem may also load the fetched physical address into one or more ofthe arrays of the TLB. Furthermore, one or more steps of the page walk,in one or more embodiments, are also installed in the arrays of the PageWalk Cache (PWC). That is, when a page walk is performed, variousintermediary entries of the page walk may be saved as page directoryentries in the PWC. The page walk steps cached in the PWC arrays allowthe processing system to perform subsequent page walks faster since itdoes not have to perform the cached steps of the page walk, and/or thepage walk does not need to start from the beginning.

Radix Page Translation (RPT) is a common and popular method of memoryvirtualization where the effective/virtual address space is translatedto real/physical addresses using a radix tree. RPT is an example of ahierarchical translation table mechanism. The hierarchy of tables isreferred to as dynamic address translation (DAT) tables, and for RPT,the tables are referred to as radix tables. For a RPT process, the radixtree (i.e., the radix tables) is stored in physical address space (e.g.,main memory) and the root of the tree, also referred to as the pagedirectory base, is stored in a register in the processor (CPU). Theradix page table in an embodiment is, for example, a hierarchical, datastructure that specifies the mapping between virtual page numbers andreal page numbers, virtual page numbers and virtualized real pagenumbers, or virtualized real page numbers and real page numbers.

In order to perform a radix page table walk (RPT) to convert a virtualaddress to a real address in physical memory, the processor starts atthe root or base of the radix tree and uses a set of the bits from thevirtual address as an offset into a page directory entry or table. Thepage directory entry at the specified offset points to a next-level pagedirectory entry or table. Another set of bits from the virtual addressare used to index into this entry/table and pick the next page directoryentry/table that will be used. This process continues until the last setof bits is used to find the page table entry (PTE) in the page table. Incurrent systems, this walking process through the tables is managedentirely by the processor CPU and can take a long time in part becauseof numerous exchanges between the CPU and the memory controller (MC).

One or more embodiments for speeding up RPT table walks are disclosed byincreasing the responsibility and operations performed by the memorycontroller during the table walk process. In one or more embodiments,the memory controller (MC) performs the entire table walk, reducing thenumber of exchanges between the CPU and the memory/memory controller(MC). In an embodiment, the memory controller performs the entire tablewalk, and the final page table entry (PTE), and all of the intermediateaddresses in the radix tree translation, are transmitted or sent back tothe processor (CPU) from the memory controller. This approach reduceslatency and allows for caching of the radix tree, e.g., in the Page WalkCaches (PWC), in the processor (CPU). In another embodiment, the memorycontroller (MC) performs the entire table walk and only the final pagetable entry (PTE) is sent back from the memory controller to theprocessor (CPU). This approach reduces latency and eliminates Page WalkCaches (PWC), and in an aspect eliminates Page Walk Caches (PWC) forhost translations. In one or more embodiments, the final PTE entrycontaining the desired translation is available at the processor (CPU)much sooner than existing approaches permit.

One example of radix page translation is described with reference toFIG. 3A. In this example, translation tables 404 are provided fortranslating addresses of virtual memory 402 to real addresses. Theorigin of the highest order translation table of the hierarchicaltranslation tables 404, is provided, for example, by a control register(CR3) 406. An effective or virtual address 408 is used to index intoeach table of the hierarchical translation tables 404 to determine anorigin address of the next table until, for example, a page table entry(PTE) having an address 409 of a page of physical memory 410 is located.In one example in which the translation mechanism utilizes DAT tables,the effective address is a virtual address having a plurality of indicesor offsets used to index into the translation tables.

FIG. 3B shows a further example of RPT, e.g. a table walk processthrough the radix tables, in which the highest level translation tableof the hierarchy is “indexed” by the high portion 408 a of an effectiveor virtual address 408 to locate a Table 1 entry 412 a that is used tolocate the next translation table (Table 2). That is, entry 412 a inTable 1 includes an origin address of Table 2. Similarly, a next portion408 b of the effective or virtual address 408 is used to index intoTable 2 to find a Table 2 entry 412 b having the origin address of Table3. A next portion 408 c of the effective or virtual address 408 is usedto index into Table 3 to find a Table 3 entry 412 c having an originaddress of Page Table 414 a. A next portion 408 d of the effective orvirtual address 408 is used to index into Page Table 414 a to locate apage table entry 412 d having the address of a physical memory page 416.The origin of the hierarchy of translation tables, in one embodiment,may include a table selector field for determining which of thehierarchy of translation tables, to start the translation. Thus, thetranslation may require only a subset of the hierarchy (wherein aneffective address is limited to include a predetermined number of mostsignificant bits having a zero value). A translation using fewer tableswill be faster than one using more tables.

FIG. 4 illustrates a block diagram of another example of a RPT processwhere a virtual address space is translated to physical addresses usinga radix tree, e.g., performing a table walk through the multiple levelsof the radix tree. The processor (CPU) 156 is remote from memory 162.FIGS. 5 and 6 illustrate a block diagram of the processor (CPU) 156 andmemory 162 and the exchange of data between the processor 156 and memorycontroller 161, where the memory controller 161 is associated with andlocal to memory 162. In one or more embodiments, memory 162 contains oneor more memory cards (not shown) where each memory card has a memorycontroller 161 and one or more DRAMs (not shown) to store data. In theexamples of FIGS. 4, 5 and 6, 48-bit addressing is used as an examplefor the purpose of description and not as a limitation on theillustrative embodiments. The translating process ca be practiced withan addressing system of any size (bit width) in a manner describedherein and is contemplated within the scope of the illustrativeembodiments.

In the examples of FIGS. 4, 5 and 6, the lowest 16 bits 408 e of the 48bit virtual address are the page offset (assuming a 64 KB page), andprovide the address to locate the desired, translated real address onthe page in memory. The next 8 bits 408 d are the offset into the pagetable, while the next three sets of 8 bits, 408 c, 408 b, and 408 a, areoffsets into different levels of page directories. To perform the tablewalk, portions of the virtual address 408 are sent by the processor(CPU) 156 to the memory controller (MC) 161 along with the pagedirectory base 420, which is also referred to as the page directory root420. In particular, typically all upper portions of the virtual address408 except for the page offset bits, e.g., page bits 408 e, are sent tothe memory controller 161 by the processor (CPU) 156. In the example ofFIGS. 4, 5, and 6, page directory 1-offset 408 a, page directory2-offset 408 b, page directory 3-offset 408 c, and page table offset 408d, along with the page directory root or base 420, are sent to thememory controller 161 as illustrated by 570 and 670 in FIGS. 5 and 6,respectively. That is, in one or more embodiments, the Page DirectoryEntry 1 (PDE1), which refer to the Page Directory Base 420 plus the pagedirectory 1-offset 408 a, with the offsets, e.g., 408 b, 408 c, and 408d, as shown by 570 and 670 are sent by the CPU 156 to the memorycontroller 161 at the outset of the translation. In other words, in anembodiment all the offsets (408 a, 408 b, 408 c, and 408 d) are all senttogether, and in an aspect, with the Page Directory Base 420 orsequentially with the Page Directory Base 420, from the processor 156 tothe memory controller 161 over the bus between the processor (CPU) 156and the memory 162. A new instruction is used to transmit the pagedirectory 2-offset 408 b, the page directory 3-offset bit 408 c, and thepage table offset 408 d, with the page directory 1-offset 408 a and thepage directory base 420, as in previous methods of translation both thepage directory 1-offset 408 a and the page directory root or base 420were initially transmitted by the processor 156 to the memory controller161 prior to and without the other offsets 408 b, 408 c, or 408 d.

The page directory root or base 420 is provided by the operating system,and in an aspect the page directory base 420 is based on the thread ofthe virtual address that is being translated. According to anembodiment, to perform the table walk, the page directory 1-offset 408 ais added to the page directory base 420 in and by the memory controller161, and a memory access is performed as shown at 425 in FIG. 4 to readthis memory location. In an aspect, the memory fetch 425 obtainsinformation and data from the DRAMS located on the memory card with thememory controller 161. The page directory base 420 serves to identifythe address of a table or directory and the page directory 1-offset 408a serves as an index into the table identified by the page directorybase 420. That entry in the table, e.g., the memory location identifiedby the address at that entry in the table, contains the base of thelevel-2 page directory entry, e.g., the Page Directory Table 2 Address430, for the translation. The memory fetch 425 in one or moreembodiments obtains from memory more than the indexed entry to thetranslation table, and in an aspect obtains information that will bestored in one or more caches associated with the processor, e.g., L2/L3caches. According to an embodiment where the intermediaries of thetranslation are stored in the processor 156, and in an aspect in thePage Walk Cache (PWC) in the processor 156, the PDE1 response 572 inFIG. 5 is sent from the memory controller 161 to the processor (CPU)156. The PDE1 response 572 in an aspect contains the information fetchedfrom memory at 425, and in a further aspect includes the Page DirectoryTable Address. In one or more embodiments, the Page Directory Table 2Address is stored in the PWC, and in an aspect the Page Directory Table2 Address is stored by the processor 156 in the PWC.

Continuing with the translation, the page directory 2-offset 408 b isadded to the directory base (Page Directory Table 2 Address) 430 in andby the memory controller 161, and a memory access is performed as shownat 435 in FIG. 4 to read this memory location. In an aspect, the memoryfetch 435 obtains information and data from the DRAMS located on thememory card with the memory controller 161. The Page Directory Table 2Address 430 serves to identify the address of a table or directory andthe page directory 2-offset 408 b serves as an index into the tableidentified by the page directory base 430. This memory location containsthe base of the level-3 page directory entry, e.g. the Page DirectoryTable 3 Address 440, for the translation. The memory fetch 435 in one ormore embodiments obtains from memory more than the indexed entry to thetranslation table, and in an aspect obtains information that will bestored in one or more caches associated with the processor, e.g., L2/L3caches. According to an embodiment where the intermediaries of thetranslation are stored in the processor, and in an aspect in the PageWalk Cache (PWC), the PDE2 response 574 in FIG. 5 is sent from thememory controller 161 to the processor (CPU) 156. The PDE2 response 574in an aspect contains the information fetched from memory at 435, and ina further aspect includes the Page Directory Table 3 Address. In one ormore embodiments, the Page Directory Table 3 Address is stored in thePWC, and in an aspect is stored by the processor 156 in the PWC.

Continuing further with the translation, if the virtual address 408being translated has additional offset bits that were sent to the memorycontroller 161, the page directory 3-offset 408 c is added to thedirectory base (Page Directory Table 3 Address) 440 in and by the memorycontroller 161, and a memory access is performed as shown at 445 in FIG.4 to read this memory location. In an aspect, the memory fetch 445obtains information and data from the DRAMS located on the memory cardwith the memory controller 161. The Page Directory Table 3 address 440serves to identify the address of a table or directory and the pagedirectory 3-offset 408 c serves as an index into the table identified bythe page directory base 440. This memory location contains the base ofthe page table offset entry, e.g. the Page Table Address 450, for thetranslation. The memory fetch 445 in one or more embodiments obtainsfrom memory more than the indexed entry to the translation table, and inan aspect obtains information that will be stored in one or more cachesassociated with the processor, e.g., L2/L3 caches. According to anembodiment where the intermediaries of the translation are stored in theprocessor, and in an aspect in the Page Walk Cache (PWC), the PDE3response 576 in FIG. 5 is sent from the memory controller 161 to theprocessor (CPU) 156. The PDE3 response 576 in an aspect contains theinformation fetched from memory at 445, and in a further aspect includesthe Page Table Address. In one or more embodiments the Page TableAddress is stored in the PWC, and in an aspect is stored by theprocessor 156 in the PWC.

Continuing further down the page table walk to obtain the addresstranslation, the page table offset 408 d is added to the directory base(Page Table Address) 450 in and by the memory controller 161, and amemory access is performed as shown at 455 in FIG. 4 to obtain the PageTable Entry (PTE) 460. In an aspect, the memory fetch 455 obtainsinformation and data from the DRAMS located on the memory card with thememory controller 161. The Page Table Address 450 serves to identify theaddress of a table or directory and the page table offset 408 d servesas an index into the table identified by the Page Table Address 450.This memory location contains the Page Table Entry 460 for thetranslation. The PTE response 578 in FIG. 5 is sent from the memorycontroller 161 to the processor (CPU) 156. Similarly, in the translationprocess of FIG. 6, the PTE response 678 is sent from the memorycontroller 161 to the processor (CPU) 156. The PTE response 578 and 678in an aspect contains the information fetched from memory at 455, and ina further aspect includes the page table entry (PTE) 460. In one or moreembodiments the page table entry (PTE) 460 is stored in the TLB, and inan aspect is stored by the processor 156 in the TLB.

In one or more embodiments, as illustrated in FIGS. 5 and 6, all theoffsets into the directory tables along with the Page Base Rootdirectory are sent from the processor to the memory controller,preferably at the initiation of the table walk process, and preferablytogether. The memory controller instead of the processor in one or moreembodiments performs the table walk, e.g., the memory controller addsthe offsets to the base tables/directories, and the memory accessesemanate from the memory controller. That is the memory controller willread memory, e.g., the DRAMs, and add the offsets. In both approaches ofFIGS. 5 and 6, the memory controller performs the pointer chasingprocess during translation instead of the processor (CPU).

In the embodiment of FIG. 6, only the last memory line access, e.g.,that contains the Page Table Entry (PTE) 460, is sent back to theprocessor, and preferably is stored in the TLB in the processor. In theembodiment of FIG. 6, the intermediary memory accesses, e.g., thatcontain the intermediary directories 430, 440, and 450, are not sentback to the processor, and the intermediary directories are not storedin any Page Walk Caches (PWCs). In the embodiment of FIG. 5, one or moreof the intermediary memory accesses, e.g, that contain the PageDirectory Table 2 Entry/Address 430, Page Directory Table 3Entry/Address 440, and Page Directory Table Entry/Address 450, andpreferably all the intermediary memory accesses, in addition to the PageTable Entry 460, from FIG. 4 are transmitted from the memory controller161 to the processor 156. The intermediary directory entries 430, 440,and 450 contained in the intermediary memory accesses sent back to theprocessor can be stored in one or more Page Walk Caches (PWCs), whilethe Page Table Entry (PTE) can be stored in the TLB. For example, theintermediate entries (412 a, 412 b, and 412 c) of the translation ortable walk illustrated in FIG. 3B are transmitted back to the processor,and preferably are stored in the PWCs, while the page table entry 412 dfrom the translation or table walk illustrated in FIG. 3B is transmittedback to the processor and stored in the TLB. While the embodiment ofFIG. 5 illustrates all the intermediary translations, e.g., the basetables or directories, being transmitted back to the processor, it canbe appreciated that less than all and any combination of theintermediary memory accesses, e.g., the intermediary directory entries,can be transmitted back to the processor, and in an aspect stored in oneor more Page Walk Caches (PWCs).

In the FIG. 6 embodiment, the latency of processing the translationcould be reduced over the FIG. 5 embodiment in situations where thememory controller is saturated with requests, as only the PTE response678 is transmitted back to the processor. While the FIG. 6 embodimentshould complete the translation (the table walk) quicker, the processor,however does not have the benefit of the intermediary Page Tabledirectories stored in the Page Walk Caches (PWCs). Accordingly, whetherthe intermediary translations are saved in the PWC is a matter of designchoice including whether to include a cache or cache large enough tostore the intermediary directory translations in the hope of reducingfuture table walk latency.

In a typical modern microprocessor, the processor adds the offsets tothe Base directory in the processor, the processor sends the Base andOffsets, e.g., Base 420+Offset 408 a, or Base 430+Offset 408 b, tomemory to fetch the next Base, and the response, e.g., the memory accessresults, are sent back to the processor. Such a memory access exchangeis on the order of 300 cycles, so to traverse the table walk of FIG. 4with such a system configuration would take on the order of 1200 cycles.In a virtualized environment as shown in FIG. 2B where the guestoperating system implements a radix page translation tree on top of thehypervisor's Radix Page Table, a single guest translation could requirenumerous memory exchanges between the processor and memory, for example24 memory exchanges totaling 7200 cycles. In the embodiments where thetranslation is performed in the memory controller, those memory accessexchanges between the processor and memory are eliminated reducing thelatency involved in the table walk process. There is still a memoryaccess to obtain the information that is residing in memory, but thosememory accesses are controlled by the memory controller that is localto, and often on the same card, as the memory devices, e.g., the DRAMs.In other words, the memory fetch request does not emanate from theprocessor and does not have to traverse the bus between the processorand memory.

The benefit of the two approaches is that the number of exchanges backand forth between the processor and the memory/memory controller arereduced. The system and translation process according to theseembodiments do not incur as many round trip exchanges between theprocessor and the memory/memory controller and thus do not incur thelatency associated with traversing the bus between the processor 156 andmemory 162 for these memory accesses. For example, in the embodiment ofFIG. 6, there preferably is one memory access request 670 sent by theprocessor 156 to the memory controller 161, and one response 678, e.g.,the memory access line containing the page table entry, sent back fromthe memory controller 161 to the processor 156. It is contemplated thatthe single response back by the memory controller to the processor willtake longer, e.g., 500 cycles, than one of the multiple memory accessesaccording to the typical technique, since there will be multipleaccesses to memory as the memory controller walks the translationsthrough the various tables/directories. That single exchange between theprocessor and memory controller however will reduce the total latency towalk the radix tree, e.g. to obtain the translation (the PTE 460).

The translation process illustrated in FIG. 5 can in one or moreembodiments consume the same bandwidth as existing table walk processesand take longer than the translation process of FIG. 6, but still reducelatency over existing techniques while having the benefit of theintermediary addresses (intermediary tables/directories) stored in thePage Walk Caches in the processor. Sending the intermediary addressesfor the intermediary tables and directories from the memory controllerback to the processor could slow the translation process of FIG. 5compared to FIG. 6, but likely not significantly. It is contemplated inan embodiment that transmitting each of the intermediary responses, e.g.PDE response 572, PDE2 response 574, and PDE3 response 576, will takeabout 60-70 cycles, but would be less than the 300 cycles to performeach round trip exchange between the processor and memory. In one ormore embodiments, the memory controller can be aware of the presence orabsence of the intermediate addresses in the CPU cache, e.g., in PageWalk Tables (PWCs), and in one or more aspects the memory controller cansend only the required memory lines. In this manner, the benefits ofcaching the intermediate addresses, e.g., for the intermediatetables/directories, in a Page Walk Cache (PWC) are preserved, but thelatency of any table walk that does not hit in the last level Page WalkCache (Page Directory Table 3 Address 440 in FIG. 4) will be improved.

While the embodiments of the address translation process in FIGS. 5 and6 illustrate a single level translation, e.g., single level translationof a virtual address to a real address, the address translationprocesses of FIGS. 5 and 6, and combinations thereof, can also be usedin nested translations. In nested translations, for example where avirtual machine hosts a guest as shown in FIG. 2B, where a guest processuses radix translation running on a host running radix translation,there will be multiple levels of RPT. The guest translation will haveintermediate translations, e.g., PDE2, PDE3 and PTE addresses, and thePDE2, PDE3, and PTE addresses associated with each memory access for theguest (the PDE2, PDE3 and PTE for the host level). By utilizing thetranslation process of FIGS. 5 and 6 on the various guest and host leveltranslations, further reduction of latency in translation can beachieved. The nested translation can also use combinations of theprocesses of FIGS. 5 and 6. For example, the intermediate information,e.g., the entries in the Page Walk Cache and/or TLB, for the hosttranslation will not be stored as illustrated in part by the process ofFIG. 6, while the intermediate information, e.g., the entries in thePage Walk Cache, will be stored for the guest as illustrated by theprocess of FIG. 5. That is the intermediaries are not stored for thehost translation memory accesses but the intermediaries are stored forthe guest translation memory accesses. By utilizing this hybrid approachfor nested address translations the footprint would be reduced bycreating the appearance of only one level of translation by not storingany intermediate information, e.g., no intermediate directory addresses,for the host translations, while storing the intermediate informationfor the guest translations. The reduction in footprint could offset anylosses from not storing the intermediate addresses for the host becauseof area reduction, power reduction and better utilization of the TLB forguest translation that continue to be cached. For example, a virtualizedsystem where a guest is running on a host, it could become necessaryunder existing processes to store 18 PWC entries and 6 TLB entries forone nested translation, whereas utilizing the hybrid (combined) approachonly 3 PWC entries and a six TLB would be stored thus saving processorarea reduction and power reduction.

FIG. 7 is an exemplary flowchart in accordance with one embodimentillustrating and describing one or more methods of handling data,including in an embodiment, processing address translations, e.g., RadixPage Translations (RPT) in accordance with one or more embodiments ofthe present disclosure. More specifically, the disclosed methods in anaspect are directed to performing a table walk to obtain an addresstranslation preferably with the memory controller performing the tablewalk. While the method 700 is described for the sake of convenience andnot with an intent of limiting the disclosure as comprising a seriesand/or a number of steps, it is to be understood that the process doesnot need to be performed as a series of steps and/or the steps do notneed to be performed in the order shown and described with respect toFIG. 7, but the process may be integrated and/or one or more steps maybe performed together, simultaneously, or the steps may be performed inthe order disclosed or in an alternate order.

The method 700 in FIG. 7 relates to processing data in an informationhandling system, and more particularly to processing addresstranslations, for example virtual addresses to real addresses in avirtualized memory system, including in embodiments processing nestedaddress translations. In an information handling system, the processorhandles instructions including requests to load data from memory. Oftenthe requests or instructions to load data from memory include virtualaddresses to the location(s) in memory where the required data islocated and those virtual addresses need to be translated into realaddresses in the physical memory devices. A request for an addresstranslation is made at 705. The request for address translation could befrom an instruction decoded and issued to the processor. At 710, theprocessor sends the base directory and the virtual address offsets tothe memory controller. In one or more embodiments, at 710, the processorsends all the virtual memory offsets to the memory controller together,preferably with the base directory. In an embodiment, at 710, theprocessor adds the first level virtual address to the base directory andsends the combined base directory and first level offset to the memorycontroller with the remaining virtual memory offsets. It can beappreciated that all the virtual memory offsets except for the pagebits, e.g., all the virtual address bits except for the address bitsspecifying the location on the page of memory, can be sent from theprocessor to the memory controller.

At 715, in one embodiment, the memory controller adds the Offset sent bythe processor to the base directory. In the first instance of addresstranslation, the first level offset is added to the base directory at715. In the instance where the processor added the first level offset tothe base directory, the memory controller does not perform thiscombination. At 720 the memory controller accesses memory for the memoryline indicated by the base and offset. In one or more embodiments, thememory controller combines or adds the offset to the directory table,e.g., uses the offset and the current directory table or base to look-upand fetch the next directory table. If this is the first level of memorytranslation, the memory controller accesses memory for the memory lineindicated by the base and the first level offset. As discussed above,the offset bits in an aspect represent an index into the directorytable, and the memory controller accesses memory at 720 for the memoryline corresponding to the entry in the directory table. In anembodiment, the memory line read by the memory controller contains theaddress for the next directory table. In one or more embodiments thememory controller extracts the address for the next directory table asthe memory line read from memory might contain a chunk of data includingmore than just the directory table address.

At 730, it is determined whether the translation process is saving theintermediate base directory addresses. If the system is saving theintermediate Directory Table addresses (730: Yes), then at 735 thememory line accessed by the memory controller at 720 is sent back to theprocessor. In an aspect the entire memory line is sent back to theprocessor at 735, or in one or more embodiments, the intermediaryDirectory Table address is sent back to the processor. At 740, theintermediary Directory Table Address is saved in the Page Walk Cache inthe processor. In an aspect, where the memory line sent back to theprocessor has more data than just the Directory Table address, theprocessor extracts and saves the address for the intermediary DirectoryTable address in the Page Walk Cache. The process after 740 continues to750.

At 730, if it is determined that intermediate Directory Tables are notbeing saved (730: No), then the process continues to 750 where it isdetermined whether there are any additional offsets in the virtualaddress received by the memory controller. Thus if the translationprocess is operating according to the embodiment of FIG. 6, the processwould proceed from 730 to 750, skipping steps 735 and 740. If at 750 itis determined that there are additional offset to the virtual address(750: Yes), then the process proceeds back to step 715, where the memorycontroller adds the offset to the Directory Table. In the instance wherethe process is returning to process step 715, the Directory Table towhich the next level offset is added (is indexed into) is the DirectoryTable that is at the address returned from the memory access at 720, andin an aspect, the address specified by the entry identified in theprevious Directory Table. The memory controller thereafter proceeds to720 where the memory controller accesses (reads) memory again this timefor the memory line containing the next Directory Table. The processcontinues through steps 715, 720, 730, 735, and 740 until at 750 thereare no more virtual address offsets (750: No). In other words, theprocess 700 continues until the table walk is complete at 750.

If at 750 there are no more virtual address offsets (750: No), the tablewalk is complete and at 755 the memory line from the memory access at720 is sent to the processor. In an embodiment the Page Table Entry(PTE) can be extracted from the memory line read at 720 and the PTE canbe sent to the Processor. At 760 the PTE is saved in the TLB in theprocessor. In the situation where the memory line sent back to theprocessor at 755 contains more than just the PTE, the processor extractsthe PTE and stores it in the TLB at 760. Future requests for thisaddress translation should hit in the TLB.

While the illustrative embodiments described above are preferablyimplemented in hardware, such as in units and circuitry of a processor,various aspects of the illustrative embodiments may be implemented insoftware as well. For example, it will be understood that each block ofthe flowchart illustrations in FIG. 7, and combinations of blocks in theflowchart illustration, can be implemented by computer programinstructions. These computer program instructions may be provided to aprocessor or other programmable data processing apparatus to produce amachine, such that the instructions which execute on the processor orother programmable data processing apparatus create means forimplementing the functions specified in the flowchart block or blocks.These computer program instructions may also be stored in acomputer-readable memory or storage medium that can direct a processoror other programmable data processing apparatus to function in aparticular manner, such that the instructions stored in thecomputer-readable memory or storage medium produce an article ofmanufacture including instruction means which implement the functionsspecified in the flowchart block or blocks.

Accordingly, blocks of the flowchart illustration support combinationsof means for performing the specified functions, combinations of stepsfor performing the specified functions, and program instruction meansfor performing the specified functions. It will also be understood thateach block of the flowchart illustration, and combinations of blocks inthe flowchart illustration, can be implemented by special purposehardware-based computer systems which perform the specified functions orsteps, or by combinations of special purpose hardware and computerinstructions.

One or more embodiments of the present disclosure may be a system, amethod, and/or a computer program product. The computer program productmay include a computer readable storage medium (or media) havingcomputer readable program instructions thereon for causing a processorto carry out aspects of the present disclosure.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present disclosure may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present disclosure.

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay be executed substantially concurrently, or the blocks may sometimesbe executed in the reverse order, depending upon the functionalityinvolved. It will also be noted that each block of the block diagramsand/or flowchart illustration, and combinations of blocks in the blockdiagrams and/or flowchart illustration, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts or carry out combinations of special purpose hardware and computerinstructions.

Moreover, a system according to various embodiments may include aprocessor and logic integrated with and/or executable by the processor,the logic being configured to perform one or more of the process stepsrecited herein. By integrated with, what is meant is that the processorhas logic embedded therewith as hardware logic, such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), etc. By executable by the processor, what is meant is that thelogic is hardware logic; software logic such as firmware, part of anoperating system, part of an application program; etc., or somecombination of hardware and software logic that is accessible by theprocessor and configured to cause the processor to perform somefunctionality upon execution by the processor. Software logic may bestored on local and/or remote memory of any memory type, as known in theart. Any processor known in the art may be used, such as a softwareprocessor module and/or a hardware processor such as an ASIC, a FPGA, acentral processing unit (CPU), an integrated circuit (IC), a graphicsprocessing unit (GPU), etc.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the embodiments of the present disclosure has beenpresented for purposes of illustration and description, but is notintended to be exhaustive or limited to the embodiments in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art without departing from the scope and spiritof the disclosure. The embodiments and examples were chosen anddescribed in order to best explain the principles of the disclosure andthe practical application, and to enable others of ordinary skill in theart to understand the disclosure for various embodiments with variousmodifications as are suited to the particular use contemplated.

The programs described herein are identified based upon the applicationfor which they are implemented in a specific embodiment of thedisclosure. However, it should be appreciated that any particularprogram nomenclature herein is used merely for convenience, and thus thedisclosure should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will be further appreciated that embodiments of the presentdisclosure may be provided in the form of a service deployed on behalfof a customer to offer service on demand.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. An information handling system comprising: aprocessor for processing data; one or more memory devices having aplurality of locations for storing the data, each location having aphysical address; a Page Walk Cache (PWC) for storing a plurality ofpage directory entries; a memory controller configured to controlreading and writing accesses to the one or more memory devices; whereinthe processor, in response to a request to translate a first virtualaddress to a second address, is configured to: send from the processorto the memory controller a page directory base and a plurality of memoryoffsets, wherein the plurality of memory offsets includes at least afirst level memory offset and a second level memory offset; and receivefrom the memory controller at least one of the plurality of pagedirectory entries; and store in the PWC the at least one of theplurality of page directory entries; and wherein the memory controlleris configured to: receive from the processor a page directory base and aplurality of memory offsets; read from the one or more memory devices afirst level page directory entry using the page directory base and thefirst level memory offset; combine the first level page directory entrywith the second level memory offset; read from the one or more memorydevices a second level page directory entry using the first level pagedirectory entry and the second level memory offset; and send to theprocessor at least one of the plurality of page directory entries. 2.The information handling system of claim 1, wherein in response todetermining that all the plurality of memory offsets have been combinedwith the plurality of page directory entries, the memory controller isconfigured to send a page table entry (PTE) to the processor.
 3. Theinformation handling system of claim 1, wherein the memory controller isconfigured to send the first level page directory entry to theprocessor.
 4. The information handling system of claim 1, wherein thememory controller is configured to send the first level page directoryentry and the second level page directory entry to the processor.
 5. Theinformation handling system of claim 1, wherein the processor isconfigured to combine the page directory base and the first leveloffset, and to send the plurality of memory offsets together with thecombined page directory base and first level offset to the memorycontroller.
 6. The information handling system of claim 1, wherein thememory controller is local to the one or more memory devices and isfurther configured to fetch from the one or more memory devices a memoryline containing an address of the first level page directory entry. 7.The information handling system of claim 6, wherein the memorycontroller is further configured to extract from the memory linecontaining the address of the first level page directory entry, theaddress of the first level page directory entry.
 8. The informationhandling system of claim 6, wherein the system is further configured totransmit the memory line containing the address of the first level pagedirectory entry from the memory controller to the processor, and whereinthe processor is further configured to extract from the memory linecontaining the address of the first level page directory entry, theaddress of the first level page directory entry.
 9. The informationhandling system of claim 8, wherein the processor is further configuredto store in the PWC the first level page directory entry.
 10. Theinformation handling system of claim 6, wherein the memory controller isfurther configured to fetch from the one or more memory devices a memoryline containing an address of the second level page directory entry. 11.The information handling system of claim 10, wherein the memorycontroller is further configured to extract from the memory linecontaining the address of the second level page directory entry, theaddress of the second level page directory entry.
 12. The informationhandling system of claim 10, wherein the system is configured totransmit the memory line containing the address of the second level pagedirectory entry from the memory controller to the processor, and theprocessor is further configured to extract from the memory linecontaining the address of the second level page directory entry, theaddress of the second level page directory entry.
 13. The informationhandling system of claim 12, wherein the processor is further configuredto store in the PWC the first level page directory entry and the secondlevel page directory entry.
 14. The information handling system of claim1, wherein, on condition that the memory controller receives the pagedirectory base and the plurality of memory offsets, the memorycontroller is configured to control all the memory reading operationsfor the plurality of page directory entries stored in memory and thesystem is configured so that all the memory reading operations for theplurality of page directory entries stored in memory originate in thememory controller.
 15. The information handling system of claim 1,wherein the system is configured so that all the plurality of memoryoffsets are transmitted together from the processor to the memorycontroller.
 16. The information handling system of claim 1, wherein thememory controller is configured to combine the page directory base andfirst level offset.
 17. The information handling system of claim 1,wherein the memory controller is configured to transmit a page tableentry (PTE) from the memory controller to the processor, wherein the PTEcontains the translation of the first virtual address to the secondaddress.
 18. The information handling system of claim 1, wherein thesystem is further configured to send a memory line from the memorycontroller to the processor that contains an address of a page tableentry (PTE), and, wherein the processor is further configured to extractfrom the memory line containing the address of the page table entry(PTE), the page table entry (PTE).
 19. The information handling systemof claim 1, wherein the memory controller is local to the one or morememory devices and is further configured to combine a third level offsetwith the second level page directory entry and to read from memory athird level page directory entry using the third level offset and thesecond level page directory entry.
 20. The information handling systemof claim 1, wherein the request to translate comprises a nestedtranslation having a guest virtual address and a host virtual address.